The invention relates generally to catheters and endoscopes and other inspection instruments, and more particularly to guidance and viewing systems for catheters and endoscopes and other inspection instruments.
Optical coherence domain reflectometry (OCDR) is a technique developed by Youngquist et al. in 1987 (Youngquist, R. C. et al., xe2x80x9cOptical Coherence-Domain Reflectometry: A New Optical Evaluation Technique,xe2x80x9d 1987, Optics Letters 12(3):158-160). Danielson et al. (Danielson, B. L. et al., xe2x80x9cGuided-Wave Reflectometry with Micrometer Resolution,xe2x80x9d 1987, Applied Physics 26(14): 2836-2842) also describe an optical reflectometer which uses a scanning Michelson interferometer in conjunction with a broadband illuminating source and cross-correlation detection. OCDR was first applied to the diagnosis of biological tissue by Clivaz et al. in January 1992 (Clivaz, X. et al., xe2x80x9cHigh-Resolution Reflectometry in Biological Tissues,xe2x80x9d 1992, Optics Letters 17(1):4-6). A similar technique, optical coherence tomography (OCT), has been developed and used for imaging with catheters by Swanson et al. in 1994 (Swanson, E. A. et al., U.S. Pat. Nos. 5,321,501 and 5,459,570). Tearney et al. (Tearney, G. J. et al., xe2x80x9cScanning Single-Mode Fiber Optic Catheter-Endoscope for Optical Coherence Tomograph,xe2x80x9d 1996, Optics Letters 21(7):543-545) also describe an OCT system in which a beam is scanned in a circumferential pattern to produce an image of internal organs. U.S. Pat. No. 5,570,182 to Nathel et al. describes method and apparatus for detection of dental caries and periodontal disease using OCT. However, as OCT systems rely on mechanical scanning arms, miniaturizing them enough to leave room for other devices in the catheter is a serious problem.
Polarization effects in an OCDR system for birefringence characterization have been described by Hee et al. (Hee, M. R. et al., xe2x80x9cPolarization-sensitive low-coherence reflectometer for birefringence characterization and ranging,xe2x80x9d J. Opt. Soc. Am. B, Vol. 9, No. 6, June 1992, 903-908) and in an OCT system by Everett et al. (Everett, M. J. et al., xe2x80x9cBirefringence characterization of biological tissue by use of optical coherence tomography,xe2x80x9d Optics Letters, Vol. 23, No. 3, Feb. 1, 1998, 228-230).
In a prior art OCDR scanning system 10, shown in FIG. 1, light from a low coherence source 12 is input into a 2xc3x972 fiber optic coupler 14, where the light is split and directed into sample arm 16 and reference arm 18. An optical fiber 20 is connected to the sample arm 16 and extends into a device 22, which scans an object 24. Reference arm 18 provides a variable optical delay. Light input into reference arm 18 is reflected back by reference mirror 26. A piezoelectric modulator 28 may be included in reference arm 18 with a fixed mirror 26, or modulator 28 may be eliminated by scanning mirror 26 in the Z-direction. The reflected reference beam from reference arm 18 and a reflected sample beam from sample arm 16 pass back through coupler 14 to detector 30 (including processing electronics), which processes the signals by techniques that are well known in the art to produce a backscatter profile (or xe2x80x9cimagexe2x80x9d) on display 32.
This invention is a device which is incorporated into a catheter, endoscope, or other medical device to measure the location, thickness, and structure of the arterial walls or other intra-cavity regions at discrete points on the medical device during minimally invasive medical procedures. The information will be used both to guide the device through the body and to evaluate the tissue through which the device is being passed. Multiple optical fibers are situated along the circumference of the device. Light from the distal end of each fiber is directed onto the interior cavity walls via small diameter optics (such as gradient index lenses and mirrored corner cubes). The light reflected or scattered from the cavity walls is then collected by the fibers which are multiplexed at the proximal end to the sample arm of an optical low coherence reflectometer. The resulting data, collected sequentially from the multiple fibers, can be used to locate small structural abnormalities in the arterial or cavity wall (such as aneurysms or arteriovenous malformations) that are currently not resolvable by existing techniques. It also provides information about branching of arteries necessary for guiding of the device through the arterial system. Since only the periphery of the catheter device is used for sensing, the central region maintains usefulness for other diagnostic or surgical instruments. This device can be incorporated into standard medical catheters, endoscopes, or other medical devices, such as surgical laser fibers, angioplasty balloons, intravascular ultra-sound probes, colonoscopes, and any other device which is traversing the body. Similarly, the invention may be implemented in non-medical inspection devices.
This invention is an optical guidance and sensing system for catheters, endoscopes and o other devices based on a multiplexed optical coherence domain reflectometer (OCDR). By multiplexing between a number of sensor fibers with an optical switch, the OCDR system of the invention has multiple sequentially accessed sensor points consisting of the tip of each multiplexed fiber. These sensor points measure the scattering of light as a function of distance from the fiber tip, thus determining both the distance between the fiber tip and the nearest tissue and any structure in that tissue.
These fibers can be placed anywhere in the catheter with their tips ending at the locations where sensing is to occur. For guiding purposes, a number of fibers could be placed in a ring around the catheter wall (or embedded in it) with their tips at the distal end of the catheter. Miniature collimating and reflection optics can be used to deflect the light from the fiber tips toward the vascular walls, thus sensing any branching of the vasculature or abnormalities in the walls.